In the prior art, it is common to use plates, boards or sheets of various forms of mica in open air resistance heaters. Typically, a resistance wire is wrapped around the mica boards and mounted in a heater frame. The techniques used to wind the wire around the mica boards are well known, as is the technique for delivering power to the heating element terminals by a direct connection using insulated lead wires.
One problem with these types of mica board heaters is the number of manufacturing steps needed to make the heater. Presently, metal clips are first attached to the mica boards by riveting in a separate operation. Then, the resistance wire is wound around the mica board to form the subassembly of mica board and resistance wire. This operation is time consuming since a separate and distinct manufacturing step is required for attaching the clips to the mica boards.
Another problem with these types of heaters is the inability to use push on terminals for connection purposes. These heaters are designed with either mica terminal plates or metal terminal plates to electrically isolate energized wires and/or components. In either instance, electrical connection is accomplished by riveting terminals to the mica plate and the end of the resistance wire, which is a highly undesirable connection. Push on terminals cannot be used since mica is not strong enough to withstand the force required to properly connect a push on terminal.
Accordingly, a need exists to eliminate the weak and unreliable connections used in the prior art and extra manufacturing steps. The present invention responds to this need by providing a clip as part of a heater subassembly that removes the additional and separate step of riveting the clip to the mica board. The present invention also eliminates the need for riveting terminals to the mica board and ends of resistance wires. The present invention also provides a subassembly, which improves manufacturing by substituting welding for riveting when making electrical connections as part of a heater. The present invention also overcomes the inability to use push on terminals with mica board heaters.